384 Royal Sociely : — 



An account of the observations made during the recent fog adds 

 the force of demonstration to others recorded in the paper, that fogs 

 possess no such power of stifling sound as that hitherto ascribed 

 to them. Indeed the melting away of fog on December 13 was 

 accompanied by an acoustic darkening of the atmosphere so great 

 that at a point midway between the eastern end of the Serpentine, 

 where a whistle was sounded, and the bridge, the sound possessed 

 less than one fourth of the intensity which it possessed on the day 

 of densest fog. 



Thus, I think, has been removed the last of a congeries of errors 

 which for more than a century and a half have been associated with 

 the transmission of sound by the atmosphere. 



ROYAL SOCIETY. 



[Continued from p. 312.] 



JS T ov. 27, 1873. — W. Spottiswoode, M.A., Treasurer and Vice-Pre- 

 sident, in the Chair. 



The following communication was read : — 



" Researches in Spectrum- Analysis in connexion with the Spec- 

 trum of the Sun." — Part III. By J. J^orman Lockyer. 



The paper commences with an introduction, in which the general 

 line of work since the last paper is indicated. Eoughly speaking, 

 this has been to ascertain the capabilities of the new method in 

 a quantitative direction. It is stated that while qualitative spec- 

 trum-analysis depends upon the positions of the lines, quantitative 

 spectrum-analysis on the other hand depends not on position but 

 on the length, brightness, and thickness of the lines. 



The necessity of maps carefully executed and showing the in- 

 dividuality of each line is shown ; and it is stated that the execu- 

 tion of these maps required the use of the electric arc to render 

 the vapours of the metals incandescent. A battery of 30 Grove's 

 cells of one pint capacity was accordingly employed in the researches 

 about to be described. 



The difficulties of eye-observations of the characters of the 

 lines compelled the application of photography, another reason for 

 the use of which existed in the facility it afforded for confronting 

 spectra with each other, and so eliminating coincident lines, since 

 the lines, if due to impurities, would be longest and thickest in 

 the spectrum to which they really belonged. 



The portion of the spectrum at present worked upon is that from 

 HtoF. 



Another branch of the research has been the construction of a 

 Table of all the named Praunhofer lines, showing the lengths and 

 thicknesses of the metallic lines to the absorption of which they were 

 due ; this Table enabled the author to allocate upwards of 50 lines 



o 



in the solar spectrum, presumably overlooked by Angstrom and 

 Thalen. The Table was intended as a preliminary to a new photo- 

 graphic map of the spectrum from H to P, on a larger scale than 



